Our multifaceted investigation on normal and atypical melanocytes concerns the following topics; 1. Biologically Active 125I-MSH. 2. MSH-Receptor Hybridomas. 3. Relative Potencies of Melanotropins. 4. New Regulators of Melanin Biosynthesis and the Proliferation of Melanoma Cells. 5. Insulin and the Control of Melanoma Cell Proliferation. 6. Genetic and Biochemical Studies on Pigmented Hybrid Cells that Overexpress Typrosinase. 7. Internalization of MSH and Fine Structural Localization of Adenylate Cyclase Activity in Response to MSH. 8. The Growth of Normal Melanocytes In Vitro.